Evidence for extensive horizontal gene transfer from the draft genome of a tardigrade

Despite fascinating scientists for over 200 years, little at the molecular level is known about tardigrades, microscopic animals resistant to extreme stresses. We present the genome of a tardigrade. Approximately one-sixth of the genes in the tardigrade genome were found to have been acquired through horizontal transfer, a proportion nearly double the proportion of previous known cases of extreme horizontal gene transfer (HGT) in animals. Foreign genes have impacted the composition of the tardigrade genome: supplementing, expanding, and replacing endogenous gene families, including those families implicated in stress tolerance. Our results extend recent findings that HGT is more prevalent in animals than previously suspected, and they suggest that organisms that survive extreme stresses might be predisposed to acquiring foreign genes